Temperature control system

ABSTRACT

A heat pump is controlled during air heating operation by a twostage thermostat having its switches biased towards open positions. When the first stage switch closes, it starts the compressor of the heat pump, and adjusts the reversal valve of the heat pump to its heat position so that the indoor coil of the heat pump operates as a condenser coil to heat indoor air. When the second stage switch closes, it turns on a booster air heater, and removes the bias, moving the closing temperature of the second stage switch up to that of the first stage switch. The heat pump is controlled during air cooling operation by a second two-stage thermostat. When the first stage switch of the second thermostat closes, it starts the compressor with one cylinder unloaded. The indoor coil operates as an evaporator coil to cool the indoor air. When the switch of the second stage of the second thermostat closes, it loads the unloaded compressor cylinder, and biases the switches of the second thermostat towards closed positions, moving the closing temperature of the second stage switch of the second thermostat down to that of the first stage switch of the second thermostat.

United States Patent Primary Examiner-Charles Sukalo [72] Inventor William K. Kyle Staunton, Va. Att0rneyF. l-l. Henson [21] Appl. No. 807,610 [22] Filed Mar. 17, 1969 [45] Patented Jan. 19,1971 ABSTRACT: A heat pump 18 controlled during an heating [73] Assignee Westinghouse Electric Corporation operation by a two-stage thermostat having its switches biased Pittsburgh, Pa. towards open positions. When the first stage switch closes, it a corporation of Pennsylvania starts the compressor of the heat pump, and adjusts the reversal valve of the heat pump to its heat position so that the indoor coil of the heat pump operates as a condenser coil to heat indoor air. When the second stage switch closes, it turns on a booster air heater, and removes the bias, moving the closing temperature of the second stage switch up to that of the first [54] TEMPERATURE CONTROL SYSTEM stage switch.

12 Claims, 14 Drawing Figs. The heat pump is controlled during air cooling operation by a second two-sta e thermostat. When. the first stage switch of 52 us. Cl 165/39 the second thermism closes, it Starts the Compressor with one [51] '3" Cl F251) 29/ 0 cylinder unloaded. The indoor coil operates as an evaporator [50] Field of Search r. 165/29, 3602, co to cool the indoor air. when the Switch of the second stage of the second thermostat closes, it loads the unloaded [56] References Cited ckompressor cylingenland1 biases the switcheshof the second t ermostat towar s c ose positions, moving t e c osing tem- UNITE]? STATES PATENTS perature of the second stage switch of the second thermostat 2,806,674 9/1957 Blehn 165/29 down to that of the first stage switch of the second thermostat.

OFM um I 2 OF 1 2 I; OO s IG OUTDOOR RVS INDQOR REVERSAL I 23 VALVE Rv 62 v 05 04 cu AM'WWQMMM 13710 BH 1 l 24 EXPANsm COMPRESSOR c I5 VALVE I9 EV 20 la I CHECK VALVE MANIFOLD PATENIEDJANIQIQYI 3556203 sum 2 OF 3 FIG.|O. 1.2 cuss CM V II cR\s CMS H S! c I H 4 HR FIRST .STAGE TSWITCH OF THE HEVRMOSTAT HT HCR m 7 0| 29 B HR sF|$8fiQ?- T J T THERMOSTAT HT I BHRS an FIRST STAGE SECOND STAGE SWITCH OF THE THERMOSTAT CT H as HRI P5 34 3s V CB j R2 7 '03 c 31 as W ILS INVENTOR= WILLIAM K. KYLE,

sv a

ATTORNEY PAT BJ MQTM- v "3556203 SHEET 3 OF 3 AVERAGE CONTROL TEMPERATURE OF FIRST STAGE RooM TEMPERAT URE AvERAsE CONTROL TEMPERATURE OF SECOND STAGE FIG.I2.

AVERAGE CONTROL TEMPERATURE OF FIRST STAGE A A A A A A A AVERAGE CONTROL TEMPER TURE OF SECOND STAGE A A A A AVE AGE CONTROL AVERAGE coMTRo OF FIRST STAGE TEMPERATURE TEMPERATURE OF sEcoN sTAeE L n A I RooM TEMPERATURE ROOM TEMPERATURE AVERAGE CONTROL TEMPERATURE AVERAGE CONTROL A A A A A A A A A OF FIRST STAGE TEMPERATURE OF SECOND STAGE INVENTOR= WILLIAM K. KYLE, BY WJ'F ATTORNEY RooM TEMPERATURE TEMPERATURE con'rnot'svsram ascxonouuo em: INVENTION Y 1 c I The said of the invention s st... heating and cooling systems whichuse two-stage, heat control thermostatsfand FIG. ll is a time-temperature chart. showing the heat operation ofthe heat pumpas it would be without the use of this invention;

FIG. 12 a chart similar to that of FIG. 11, showing the heat i operation of the heat pump using this invention;

two-stage cool control thermostats. The first stage switch of a heat control thermostat turns on heat ata temperature which may ,be 72 F. Thesecondstageswitch of the heat control thermostat turns on additional heat when the temperature has dropped about 2 F? below'the control temperature of the first stage switch of the heat control thermostat, so that it is about 2 F.,colderouriiig control by the second'stage switch of the I switch 'of therlat ter. The first stage switch of a cool control thermostat providescooling at a temperature which may be 1 V I suMMAnYor THE iivvizivriou A heat pump is controlled during heating operation bya twosstage thermostat having .a heater resistor normallyenersi by s o mall db l t v Qf' mrm y si s z relay. The heater resistor biases the switches of the thermostat towards open positions. When the first stage switch closes at,

for example, 72 F it startsthe compressor of the heat pump, energizes a solenoid which adjusts the, reversal valve'of the 7 heat control thermostat than duringcontrol by the stage I FIG. 13 is a time-temperature chartshowing the cooling operation of the heat pump as it would be without the use of this invention, and 1 no. 4 is a view similar to that or FIG. 13, showing the cooling operation of the heat pump using this invention.

7 DESCRIPTION or Tris rnizrsnaeo EMBODIMENT Referring first toFIG. I of the drawingsfa refrigerant com pressor C having cylinders C 1, C 2 C} and C4, is driven by electric motor CM. The cylinder (34 is normally unloaded by a conventional unloader (not shown) adjustable to load-unload positions by solenoid LS. The outlet of the compressor C is I connected by discharge gas tube 10 to a conventional reversal valve. RV adjustable by a solenoid RV'S. The valve RV is connected by tube 11 to outdoor coil DC, by tube 12 to indoor coil IC, and by suction gas tube 13 to the inlet of the compressor CLThe outdoor coil'OC is connected by tube 15 to check heat pump to its heatposition, and partially energizes the i relay. When the second'stage switch closes at, for example. 70 F. it energizes an electric booster heater, and completes the energiza'tion of the relay. The switch of the latter opens, i

and deenergizes the heater resistor, removing the. bias on the first and second stage switches so that they close at, for example, 74F. nnd"72 F. respectively; When the secondstage switch opens,the relay remains energized until the first opening thereafter of'th'e first stage switch The heat pump is controlled during air cooling operation by "a second two-stage thermostat having a second, normally deenergized resistor heater adapted to be'energized by a nort mally open switch,,whe'n closed, of a normally deenergized,

' second relajyQWhen the lfirststageswitch of t hesecond ther mostat closes at, for example]? F., it tums on the compressor, one cylinder of which is unloaded, and partially energizes the second relay. When the second stage switch of the second thermostat closes at, for example,76 F., it energizes a soleacid, which loads, the unloaded, compressor, cylinder, and

closes its switch, energizing the second heater resistor which biases the switches of the second thermostat towards, closed positions so that the firststage switch of the latter closes at 72 valve manifold 16 which is connected by tube 18 to the indoor coil IC, by who 19 to the inlet of expansion valve EV, and by tube 20 to the outlet of the valve EV. Fan OF driven by electric motor OFM moves outdoor air over the surface of the coil OC. 'Fan IF driven by electric motorIFM moves indoor air I over the surface of the coil IC. An electric booster heater Bl-I is located adjacent to anddownstreamwith respect to airflow of the indoor coil IC. v v- The manifold 16 is that disclosed; in detail in the U.S. Pat. NQ.3299,661 of J. R. Hamish and R. W. Ayling. I The expansion valve EV is a subcooling controlvalve disclosedin detail in the U.S. Pat. No. 3,367,130 of A. Owens. It has a diaphragm chamber 22 connected by capillary tube 23 to'ther'malbulb 24in heat exch angecqntact with the tube 19.

Referring now to FIG. 2, heat control thermostat HT has a conventional, first stage, bimetallic coil with a switch arm 26 opposite switch contact 27, and has a'conventional, second stage bimetallic coil 28 with a switch arm 29 opposite switch contact 30'. A case 31 extends around thethermostat HT, and within the case 31 below the coils 25 and 28 is an electric heater resistor HRl.

Referring now to FIG. 3, cool control thermostat CT has a conventional, first stage bimetallic coil 33 with a switch arm completes the energization of the second relay. The latter FIG. 2 is a diagramm tic view of the two-stage, heat control.

thermostat used; s o s v. FIG. 3 is a diagrammatic view of the two-stage, cool control thermostatused; I t i i FIG. 4 is a diagrammatic view of the compressor motor starter; I t j I FIG. 5 is a diagrammatic view of the heat relay; i FIG. 6 is a diagrammatic view of the heat control relay; FIG. 7 is adiagrammatic view of the booster heat relay; FIG. 8isadiagrammaticview of the cool relay; FIG. 9 is a diagrammatic view of thecool control relay;

FIG. 10 is a simplified circuitschernatic of the electric controls of the heat pump;

34 opposite switch contact 35, and has a conventional, second stage, bimetallic coil 36 with a switch arm 37 opposite switch contact 38. A case 39 extends around "the thermostat CT, and within the case 39 below the coils 33'arid 36 is an electric heater resistor HR2. i Y

Referring now to FIGS. 4-9, compressor motor starter CMS has a switch CMSS which closes when the starter CMS is energized; heat relay HR has switches ll-IRSI and I-IRSZ which close'when the relay HR is energized; heat control relay l-ICR has a normally closed switch I-ICRS which opens when the relay HCR is energized; booster heat relay BI-IR-has a switch 1 BI-IRS which closes when the relay B l-IR is energized; cool relay CR has a switch CRS which closes when the relay CR is energized, and coolcontrol relay CCR- has a switch CCRS which closes when the relay CCR is energized.

The relays I-ICR and CCR are bireed relays manufactured by RBM control's', a Division of Essex Wire Co., Logansport, Ind. i

Referring now to FIG. 10, the compressor motor CM is connected in series with the starter switch CMSS to electric the lines L1 and L2; the heat relay HR and the solenoid RVS are connected :in parallel, and in series with the thermostat arm and its switch contact 27 to the lines L1 and L2; the

heat control relay I-ICR is connected in series with diode D1,

resistor R1, the switch contact 27 and the switch arm 26 to the lines L1 and L2, and in series with diode D2, the switch contact 30 and the switch arm 29 to the lines L1 and L2; the booster heat relay BHR is connected in series with the switch HRS2, the switch contact 30 and the switch arm 29 to the lines L1 and L2; the booster heat resistor BH is connected in series with the switch BHRS to the lines L1 and L2; the heater resistor HRl is connected in series with the switch HCRS to the lines L1 and L2; the cool relay CR is connected in series with the switch contact 35 and the switch arm 34 to the lines L1 and L2; the cool control relay CCR is connected in series with diode D3 and resistor R2, the switch contact 35 and the switch arm 34 to the lines L1 and L2, and in series with diode D4, the switch contact 38 and the switch arm 37 to the lines L1 and L2; the solenoid LS is connected in series with the switch contact 38 and the switch arm 37 to the lines L1 and L2, and the heater resistor HR2 is connected in series with the switch CCRS of the relay CCR to the lines L1 and L2,

HEATING OPERATION The dashed line arrows alongside the tubing of FIG. 1 show the direction of refrigerant flow during heating operation. The heater resistor HR1 is normally energized by the normally closed switch HCRS so that the thermostat coils 25 and 28 are heated to about 2 F. above room temperature, biasing the switch arms 26 and 29 towards open positions. When the first stage switch of the thermostat HT calls for heat at, for exam ple, 72 F., the switch arm 26 moves against its contact 27, energizing the heat relay HR and the solenoid RVS. The relay HR closes its switches HRSl and HRS2. The closed switch HRSl energizes the compressor motor starter CMS which closes its switch CMSS, starting the compressor motor CM. The starters for the fan motors OFM and IFM are not shown since as is conventional the fan motors would be energized when the compressor motor is energized. The solenoid RVS adjusts the reversal valve RV to its heat position. The movement of the switch arm 26 against its contact 27 also supplies current from the lines L1 and L2 through the resistor R1 and the diode D1 into the relay HCR, but the resistor R1 reduces this current below the energizing current of the relay HCR but above its dropout current so that when it is fully energized as will be described later, it will remain energized until it is completely deenergized by the switch arm 26 moving away from the contact 27.

The compressor C supplies discharge gas through the tube 10, the reversal valve RV and the tube 12 into the indoor coil IC operating as a condenser coil to heat the indoor air. Liquid flows from the coil IC through the tube 18 into the manifold 16, and from the latter through the tube 19 into the expansion valve EV. Expanded refrigerant flows from the valve EV through the tube 20 into the manifold 16, and from the latter through the tube into the outdoor coil lC operating as an evaporator coil. Refrigerant flows from the coil OC through the tube 11, the reversal valve RV and the tube 13 to the suction side of the compressor C.

If the heat provided by the indoor coil IC is insufficient, and the room temperature drops to, for example, 70 F., the second stage switch arm 29 moves against its switch contact 30. energizing through the now closed switch HRS2 of the heat relay HR, the booster heat relay BHR which closes its switch BHRS, energizing the booster heater BH. At the same time, current flows through the switch arm 29, its contact 30 and the diode D2 into the relay HCR, completing the energization thereof. The relay HCR opens its switch HCRS, deenergizing the heater resistor HRl of the thermostat HT, causing the temperature within the case 31 of the latter to decrease about 2 F. The resultant cooling of the second stage thermostat coil 28 causes its switch arm 29 to remain in contact with the switch contact 30 until the room temperature increases to 72 F. instead of to 70 F. I

When the second stage of the thermostat HT is satisfied, its switch arm 29 moves away from its contact 30, deenergizing the booster heat relay BHR, but the relay HCR remains enerthe second stage switch was moved upwardly when the switch HCRS opened and deenergized the heater resistor HRI, the switch arm 26 moves away from the switch contact 27, deenergizing the heat relay HR, the reversal valve solenoid RVS and the relay HCR. The heat relay HR opens its switches HRSl and HRS2. The now open switch HRSl deenergizes the compressor motor starter CMS which opens its switch CMSS, stopping the compressor motor CM. The now open switch HRS2 disconnects the booster heat relay BHR from the switch contact 30. The now deenergized relay HCR closes its switch HCRS, reenergizing the heater resistor HRl which heats the thermostat coils 25 and 28, restoring the operating points of the first and second stage switches of the thermostat to 72 F. and F., respectively. Thereafter, until the second stage switch of the thermostat HT again closes, the first stage switch cycles at 72 F. I

While but one booster heater has been disclosed, other booster heaters controlled as disclosed in the US. Pat. No. 2,806,674 ofG. L. Biehn, or in the copending application, Ser. No. 695,243, filed Jan. 2, i968, of W. K. Kyle and E. H. Jensen.

FIG. 11 shows the heat fluctuations without the use of this invention, and FIG. 12 shows the heat fluctuations using this invention.

COOLING OPERATION The solid-line arrows alongside the tubing of FIG. 1 shows the direction of refrigerant flow during cooling operation. The heater resistor HR2 of the cool thermostat CT is normally deenergized so that normally there is no offset of its first and second stage switches. When the first stage of the thermostat CT calls for cooling at, for example, 74 F., its switch arm 34 moves against its contact 35, energizing the cool relay CR, and supplying current through the resistor R2 and the diode D3 through the cool control relay CCR, which current is insufficient to energize the latter. The relay CR closes its switch CRS, energizing the compressor motor starter CMS which closes its switch CMSS, starting the compressor motor CM. Discharge gas flows from the compressor C through the tube 10, the reversal valve RV, and the tube 11 into the outdoor coil 0C operating as a'condenser coil. Liquid flows' from the I coil OC through the tube 15 into the manifold 16, and from the latter through the tube 19 into the inlet of the expansion valve EV, and from the outlet of the latter, through the tube 20 into the manifold 16, and from the latter through the tube 18 into the indoor coil IC operating as an evaporator coil to cool the indoor air. Refrigerant flows from the coil 1C through v cooling by the indoor coil IC. The movement of the switch arm 37 against the contact 38 also supplies additional current through the diode D4 into the cool control relay CCR energizing the latter which closes its switch CCRS, energizing the heater resistor HR2 of the thermostat CT. Heat from the resistor HR2 biases the switch arm 37 towards contact 38, causing it to remain in contact'with the contact 38 until the room temperature decreases to 74 F., the setting of the first stage switch of the thermostat CT before the relay CCR was energized. Heat from the resistor HR2 also biases the first stage switch arm 34 towards its contact 35, resetting the first stage switch of the thermostat CT to 72 F. operation where it cycles only once since its first opening dcenergizes the relay CCR which opens itscontactCCRS, deenergiz ing the heater resistor HR2. The relay CCR remains energized during the cycling of the second stage switch of the thermostat CT. When A the second stage switch of the thermostat CT is satisfied, the

second stage switch arm37 moves away from its contact 38, opening the energizing circuit of the solenoid LS, unloading the compressor cylinder C4, and discontinuing the supply of current through the diode D4 into the relayiCCR which, however, remains energizeduntil the first opening of the first stage switch of the thermostat CT. When the first stage switch of the thennostat CT is satisfied, 'it deenergizes the compressor motor starter QMS which opens its switch CMSS, stopping the compressor motor CM, and deenergizes the relay CCR which.

a two-stage, heat control thermostat having a first stage switch, and a second stage switch; 7 e first, normally active, bias means for moving said switches towards open positions; h

means including said first stage switch, when closed, for

energizing said first means; I

means including said second stage switch, when closed, for

energizing said second means;

means including said first and second stage switches, when closed, for making said bias means inactive, and for maintaining said bias means inactive until said first stage switch opens;

third means for cooling said air;

fourth means for increasing the cooling of saidair;

a two-stage, cool control thermostat having a first stage switch, and a second stage switch; a 1

second, normally inactive, bias-means for moving, when active, said switches of said cool control thermostat towards closed positions;

means including said first stage switch of said cool control thermostanwhen closed, for energizing said third means;

means including said second stage switch of said cool control thermostat, whenclosed, for energizing said fourth means; and

means including said first and second stage switches of said cool control thennostat, when closed, for making said second bias means active, and for maintaining said second bias means activeruntil said first stage switch of said cool control thermostat opens:

g 2. A system as claimed in claim I in which:

said first bias means comprises a normally energized heater resistor; and V said second bias means comprises a normally deenergized heater resistor.

3. A system as claimed in claim 2 in which:

said system has electric supply lines;

said first bias means comprises a normally deenergized relay having a normally closed switch connecting said normally energized resistorto said lines; and

said second bias means comprises a normally deenergized relay having a normally open switch for connecting, when closed, said normally deenergized resistor to said lines.

4. A heat pump comprising:

a refrigerant compressor having an electric driving motor;

an outdoor heat exchange coil;

an indoor heat exchange coil;

refrigerant expansion means;

means, when air heating is required, for routing refrigerant from said compressor through said indoor coil-operating as a condenser coil, and said expansion means, into said outdoor coil operating as an evaporator coil, and, when" 1 air cooling is required, for routing refrigerant from said compressor through said outdoor coil operating as a condenser coil, and said expansion means, into said indoor coil operating as an evaporator coil; an electric booster heater adjacent to said indoor coil; a two-stage, heat control thermostat having a first stage switch, and a second stage switch; first, normally active, bias means for moving said switches towards open positions; electric supply lines; means including said first switch, when'closed, for connecting said motor to said connections; means including said first and second switches, when closed, for connectingsaid heater to said lines, for making inactive said bias means, and for maintaining said bias means inactive until said first switch opens; electrically-operated means for increasing the output of said compressor; a two-stage, cool control thermostat having a first stage switch, and a second stage switch; second, normally inactive, bias means for moving when made active, said switches of said cool control thermostat towards closed positions; v means including said first switch, when closed, of said cool control thermostat for connecting said motor to said lines; and means'including said switches, when closed, of said cool control thermostat for connecting said electrically operated means to said lines, for making active said second bias means, and for maintaining said second bias means active until said first switch of said cool control thermostat opens. Y 5. A heat pump as claimed in claim 4 in which: said first bias means comprises a normally energized heater resistor; and saidsecond bias means comprises a normally deenergized heater resistor. 6. A heat pump as claimed in claim 5 in which: said first bias means comprises a normally deenergized relay having a normally closed switch connecting said normally energized resistor to said lines; and said second bias means comprises a normally deenergized relay having a nonnally open switch for con ecting, when closed, said normally deenergized resistor to said lines. 7. A heat pump comprising: a refrigerant compressor having'an electric driving motor; an indoor heat exchange coil connected to the discharge side of said compressor so as to operate as a condenser coil to heat indoor air; 7 refrigerant expansion means connected to said coil;

an outdoor heat exchange coil connected to said expansion means and to the suction side of said compressor so as to operate as an evaporator coil;

an indoor thermostat having a first stage switch, and a second stage switch; normally active bias means for moving said switches towards open positions; I electric supply lines; means including said first switch, when closed, for connecting said motor to said lines; an electric booster heater adjacent. to said indoor coil; and means including said switches, when closed, for connecting said booster heater to said lines, for making said bias means inactive, and for maintaining said bias means inactive until said first switch opens. 8. A heat pump as claimed in claim 7 in which: said bias means comprises a normally energized heater resistor.

9. A heat pump as claimed in claim 8 in which said bias means comprises a normally deenengized relay having a normally closed switch connecting said normally energized resistor to said lines.

10. A heat pump comprising: a refrigerant compressor having an electric driving motor; an outdoor heat exchange coil connected to the discharge side of said compressor so as to operate as a condenser coil; refrigerant expansion means; an indoor heat exchange coil connected to said expansion means and to the suction side of said compressor so as to operate as an evaporator coil to cool indoor air; an indoor thermostat having a first stage switch. and a second stage switch; normally inactive bias means for moving said switches,

when made active, towards closed positions; electric supply lines;

means including said first switch, when closed, for connecting said motor to said lines;

electrically operated means for increasing the output of said compressor; and v means including said switches, whenclosed, for connecting said electrically operatedmeans tosaid lines, for making active said bias means, and for maintaining said bias means active until said first switch opens.

11. A heat pump as claimed in claim 10 in which: said bias means comprises a normally deenergized heater resistor.

12. A heat pump as claimed in claim 11 in which: said bias means comprises a normally deenergized relay having 21 normally open switch for connecting, when closed, said heater re sistor to said lines. 

1. A temperature control system comprising: first means for heating indoor air; second means for increasing the heating of said air; a two-stage, heat control thermostat having a first stage switch, and a second stage switch; first, normally active, bias means for moving said switches towards open positions; means including said first stage switch, when closed, for energizing said first means; means including said second stage switch, when closed, for energizing said second means; means including said first and second stage switches, when closed, for making said bias means inactive, and for maintaining said bias means inactive until said first stage switch opens; third means for cooling said air; fourth means for increasing the cooling of said air; a two-stage, cool control thermostat having a first stage switch, and a second stage switch; second, normally inactive, bias means for moving, when active, said switches of said cool control thermostat towards closed positions; means including said first stage switch of said cool control thermostat, when closed, for energizing said third means; means including said second stage switch of said cool control thermostat, when closed, for energizing said fourth means; and means including said first and second stage switches of said cool control thermostat, when closed, for making said second bias means active, and for maintaining said second bias means active until said first stage switch of said cool control thermostat opens.
 2. A system as claimed in claim 1 in which: said first bias means comprises a normally energized heater resistor; and said second bias means comprises a normally deenergized heater resistor.
 3. A system as claimed in claim 2 in which: said system has electric supply lines; said first bias means comprises a normally deenergized relay having a normally closed switch connecting said normally energized resistor to said lines; and said second bias means comprises a normally deenergized relay having a normally open switch for connecting, when closed, said normally deenergized resistor to said lines.
 4. A heat pump comprising: a refrigerant compressor having an electric driving motor; an outdoor heat exchange coil; an indoor heat exchange coil; refrigerant expansion means; means, when air heating is required, for routing refrigerant from said compressor through said indoor coil operating as a condenser coil, and said expansion means, into said outdoor coil operating as an evaporator coil, and, when air cooling is required, for routing refrigerant from said compressor through said outdoor coil operating as a condenser coil, and said expansion means, into said indoor coil operating as an evaporator coil; an electric booster heater adjacent to said indoor coil; a two-stage, heat control thermostat having a first stage switch, and a second stage switch; first, normally active, bias means for moving said switches towards open positions; electric supply lines; means including said first switch, when closed, for connecting said motor to said connections; means including said first and second switches, when closed, for connecting said heater to said lines, for making inactive said bias means, and for maintaining said bias means inactive until said first switch opens; electrically operated means for increasing the output of said compressor; a two-stage, cool control thermostat having a first stage switch, and a second stage switch; second, normally inactive, bias means for moving when made active, said switches of said cool control thermostat towards closed positions; means including said first switch, when closed, of said cool control thermostat for connecting said motor to said lines; and means including said switches, when closed, of said cool control thermostat for connecting said electrically operated means to said lines, for making active said second bias means, and for maintaining said second bias means active until said first switch of said cool control thermostat opens.
 5. A heat pump as claimed in claim 4 in which: said first bias means comprises a normally energized heater resistor; and said second bias means comprises a normally deenergized heater resistor.
 6. A heat pump as claimed in claim 5 in which: said first bias means comprises a normally deenergized relay having a normally closed switch connecting said normally energized resistor to said lines; and said second bias means comprises a normally deenergized relay having a normally open switch for connecting, when closed, said normally deenergized resistor to said lines.
 7. A heat pump comprising: a refrigerant compressor having an electric driving motor; an indoor heat exchange coil connected to the discharge side of said compressor so as to operate as a condenser coil to heat indoor air; refrigerant expansion means connected to said coil; an outdoor heat exchange coil connected to said expansion means and to the suction side of said compressor so as to operate as an evaporator coil; an indoor thermostat having a first stage switch, and a second stage switch; normally active bias means for moving said switches towards open positions; electric supply lines; means including said first switch, when closed, for connecting said motor to said lines; an electric booster heater adjacent to said indoor coil; and means including said switches, when closed, for connecting said booster heater to said lines, for making said bias means inactive, and for maintaining said bias means inactive until said first switch opens.
 8. A heat pump as claimed in claim 7 in which: said bias means comprises a normally energized heater resistor.
 9. A heat pump as claimed in claim 8 in which said bias means comprises a normally deenergized relay having a normally closed switch connecting said normally energized resistor to said lines.
 10. A heat pump comprising: a refrigerant compressor having an electric driving motor; an outdoor heat exchange coil connected to the discharge side of said compressor so as to operate as a condenser coil; refrigerant expansion means; an indoor heat exchange coil connected to said expansion means and to the suction side of said compressor so as to operate as an evaporator coil to cool indoor air; an indoor thermostat having a first stage switch, and a second stage switch; normally inactive bias means for moving said switches, when made active, towards closed positions; electric supply lines; means including said first switch, when closed, for connecting said motor to said lines; electrically operated means for increasing the output of said compressor; and means including said switches, when closed, for connecting said electrically operated means to said lines, for making active said bias means, and for maintaining said bias means active until said first switch opens.
 11. A heat pump as claimed in claim 10 in which: said bias means comprises a normally deenergized heater resistor.
 12. A heat pump as claimed in claim 11 in which: said bias means comprises a normally deenergized relay having a normally open switch for connecting, when closed, said heater resistor to said lines. 